-`DEMetropolis` can now tune both `lambda` and `scaling` parameters, but by default neither of them are tuned. See [#3743](https://github.com/pymc-devs/pymc3/pull/3743) for more info.
-`DEMetropolisZ`, an improved variant of `DEMetropolis` brings better parallelization and higher efficiency with fewer chains with a slower initial convergence. This implementation is experimental. See [#3784](https://github.com/pymc-devs/pymc3/pull/3784) for more info.
- Notebooks that give insight into `DEMetropolis`, `DEMetropolisZ` and the `DifferentialEquation` interface are now located in the [Tutorials/Deep Dive](https://docs.pymc.io/nb_tutorials/index.html) section.
- Add `fast_sample_posterior_predictive`, a vectorized alternative to `sample_posterior_predictive`. This alternative is substantially faster for large models.
### Maintenance
- Remove `sample_ppc` and `sample_ppc_w` that were deprecated in 3.6.
